There are numerous devices for delivering medicament on the market and also patented where the medicament is arranged in a container, such as a syringe, cartridge and the like, and wherein the medicament is exposed to pressure when it is to be delivered. A very common design with for example injection devices is a generally tubular compartment having a stopper in one end of the compartment and a needle unit attached to the opposite end of the compartment.
In order to deliver a quantity of medicament, the stopper is exposed to pressure, i.e. pushed into the compartment by a pusher or plunger rod, which in many cases is performed by pressure means such as springs, which is common in automatic or semi-automatic injectors, whereby a delivery sequence is performed.
Usually the delivery sequence is triggered by a user manually pressing an activation button or a needle shield, which releases the spring acting on the plunger rod. The delivery sequence may also be triggered by the termination of a previous penetration sequence. In both instances, once the delivery sequence has been triggered, it continues until the dose is delivered, either when the medicament container is emptied or the delivery mechanism has reached a preset dose stop.
However, there may be instances when it is desirable for the user to take control over the delivery sequence. For example with injection of medicament into the tissue of the patient, it may for instance be that the injection hurts when the medicament expands into the tissue and the patient wants to take a pause without removing the injector or just wants to reduce the injection speed in order to the medicament to be absorbed by the tissue during the injection.
Some delivery devices are provided with electrically driven delivery mechanisms. For example the U.S. Pat. No. 6,474,219 discloses an injector arranged with a plunger rod acting on a stopper of a medicament container for expelling a dose of medicament through an injection needle. The plunger rod, in this case a helical compression spring that is driven forward by a piston drive comprising a nut element acting on the plunger rod, and an electrical motor driving the nut element. If the activation of the motor is controlled by the user, it is possible to stop the injection temporarily.
However, even if the above mentioned injector provides the possibility of temporarily stopping and starting the injection sequence, it is well known in art that there is a clear drawback to have medical devices depend on electric power in order for their function, and in particular to rely on electric power for delivery of the medicament. If for example the battery of the device would be depleted, it is impossible for the patient to receive a dose, which may be fatal to the patient.
A further drawback is that medicament devices operated by electrical components tend to be more expensive than purely mechanical devices. This is definitely true if the device is to be arranged with some sort of speed control means for the electrical motor in order for the user to be able to slow down, but not stop, the injection.
Other attempts have been made to solve this problem. Such solutions are shown in documents GB 2 443 390 and GB 2 071 499.
However, there is room for improvements regarding the size, the design and specially the ergonomics when manipulating the device.
There are thus a number of aspects that may be addressed with the present invention.